
(E.)—Land dnd Fresh-water Mollusca, collected during the summers of 
1873-74, in the vicinity of the Forty-ninth Parallel—Lake of the Woods 
to the Rocky Mountains. 
In referring the specimens to their types, it has been found necessary to take a 
broad view of the species, to avoid the too great multiplication of so-called specific 
names. Over the great area of the plains, every pool and river has its more or less 
distinct suite of forms. Limnza elodes is perhaps the most variable of all, and under 
this name shells have been included, from which specimens might have been selected 
very different in appearance, but which are all more or less closely connected by 
intermediate varieties. Bulinus hypnorum is probably one of the most constant in 
form, in all its localities. 
The Gasteropoda of the streams and lakes of the wooded region to the east, differ 
considerably in general facies from those of the Red River Valley and plains west of 
it, where a general increase in the thickness and robustness of the shells is found, 
and gives rise to a distinct series of varietal modifications. In the pools and swamps 
of the prairies, food and calcareous matter no doubt equally abound. Segmentina 
armigera there assumes its varietal form campestris ; Planorbis trivolvis often appears in 
its variety macrostomus ; Limnea stagnalis, and LD. elodes increase in size and weight of 
shell, and other species are similarly affected. By carefully noting the station of 
each form, and especially the nature of its food, and the probable presence or absence 
of sufiicient calcareous matter in the water ; many puzzling shells are found to be 
varieties depending on these circumstances. The names employed are chiefly those 
of the monographs in the Smithsonian Miscellaneous Collections, 
G. M. D. 
GASTEROPODA. 
Risso : 
Amunicola pallida, Hald. Lake of the Woods. 
Ammcola porata, Say. Lake of the Woods. 
Somatogeirus depressus? Tryon. 500 Mile Lake. East Fork Milk River. 
PALUDINADZ : 
Paludina decisa, Say. Lake of the Woods. 
Valvata tricarinata, Say. Lake of the Woods. East Fork Milk River (worn 
specimens, may have travelled from pools near the Cypress Hills.) 
Valvata sincera, Say. East Fork Milk River (worn specimens.) 
HELIcIDe : 
Helix striatilla, Anthony. Lake of the Woods. Dufferin. Pembina Mountain. 
Turtle Mountain. Wood Mountain. 
Heliz pulchella, Miller. Lake of the Woods, Pembina Mountain, Wood Mountain. 
Heliz limitaris, Sp. nov.—Shell conspicuously umbilicated, globosely depressed, 
solid, coarse ; whorls carinate at the periphery, and sub-carinate near the 
umbilicus, giving the mouth a distinctly rhomboidal form tn young 
